White organic light emitting materials have attracted much current interest because of their potential applications in full color displays with color filters, LEDs, as backlights for liquid crystal displays (LCDs) and in various lighting applications. An important component of LCDs is the white light emitter that comprises the back light for the display since liquid crystals (LCs) do not generate light but they may only-block it. Typically, LCDs allow 5-25% of the back light to pass through. As a result, LCD technology requires a significant amount of energy, and this is an important consideration in lightweight laptops or other display designs. An efficient and spectrally broad white light source would constitute an important contribution to LCD technology. Reference may be made to Kido, J. et al. Science 1995, 267, 1332; D'Andrade, B. D., et al. Adv. Mater. 2004, 16, 1585; Sun, Y., et al. Nature 2006, 440, 908. U.S. Pat. Nos. 4,758,818, 6,828,951, 6,870,584, 6,876,424, 6,635,903, 6,774,560.
So far, a variety of strategies have been worked out to realize white light emission. The general approach is to blend two or three fluorescent or phosphorescent dyes into a blue-light emitting polymer or a non-active polymer matrix. Polymer blend systems, such as three-polymer blends containing red-, green-, and blue-light-emitting polymers and two-polymer blends containing blue- and orange-light-emitting polymers, have also been demonstrated. Reference may be made to Kawamura, Y. et al. J. Appl. Phys. 2002, 92, 87; Gong, X. et al. Adv. Mater. 2004, 16, 615; Al Atter, H. A. et al. Appl. Phys. Lett. 2005, 86, 121101; Berggren, M. Nature 1994, 372, 444; Xu, Y. H. Appl. Phys. Lett. 2005, 86, 163 502; Ho, G. K. Appl. Phys. Lett. 2004, 85, 4076. U.S. Pat. No. 5,966,393.
Metal complexes containing Eu, Ir are another class of molecules which are used for white light emission. Reference may be made to Kim, T.-H., et al. Adv. Funct. Mater. 2006, 16, 611; Coppo, P., et al. Angew. Chem. Int. Ed. 2005, 44, 1806.
A few low molecular weight organic molecules emitting white-light is also reported. Reference may be made to Liu, Y., et al. J. Am. Chem. Soc. 2006, 128, 5592; Mazzeo, M., et al. Adv. Mater. 2005, 17, 34.
U.S. Pat. No. 4,099,089 discloses the use of terbium activated rare earth oxyhalide phosphor material alone or in combination with other suitable phosphor materials at the elevated operating temperatures to generate white light emitting composite materials.
U.S. Pat. No. 6,869,695 discloses the fabrication of a white-light emitting OLED by using the combined monomer and aggregated emission. The device employs two emitters in a single emissive region to sufficiently cover the visible spectrum.
The main drawbacks of the above-mentioned white light emitting materials, the process includes highly complicated methods resulting in very high cost.
An alternative and easy method for the production efficient white light emission will be useful for the above-mentioned applications. White light emitting organogels are not reported in literature so far. Organogels are easy to process compared to other methods for the device manufacturing. Gelation allows greater flexibility for coating. U.S. Pat. No. 5,415,993 discloses the preparation of light-sensitive photo-thermographic emulsion layers containing a thermoreversible organogel based binder.
Organogels are extensively used in the field of medicine and cosmetics. For example U.S. Pat. No. 6,914,051 discloses a penetrating antibiotic gel for treating pain, inflammation and other pathological conditions affecting musculoskeletal tissues and other soft tissues of the body. The composition includes an antibiotic compound and a mobilizing agent in an amount sufficient to enable the antimicrobial compound to penetrate into the sub-dermal soft tissues. The antimicrobial compound may be a macrolide antibiotic compound such as azithromycin, erythromycin or roxithromycuvand the mobilizing agent may be an organogel compound, such as pluronic lecithin liposomal organogel. U.S. Pat. No. 6,687,533 discloses a non-implantable CT and MRI marker composed of an organogel. U.S. Pat. No. 5,411,737 discloses a slow release drug delivery device for the prolonged administration of topically active medicines, which consists of a vehicle in which water is soluble and in which is dissolved the topically active drug which is formed into a stable organogel with a polymer matrix with a very low water absorbing capability. U.S. Pat. No. 6,737,394 discloses a detergent composition having a surfactant, a thickening agent and an organogel, which is used for cleansing the human body.
Oligo (p-phenylenevinylene) derivatives are known to form self-assembled nanostructures, which results stable organogels in nonpolar solvents at ambient conditions. They are found to act as efficient donor scaffold for excitation energy transfer and light harvesting with suitable energy acceptors. Reference can be made to A. Ajayaghosh et al., J. Am. Chem. Soc. 2001, 123, 5148; A. Ajayaghosh et al., Chem. Eur. J. 2005, 11, 3217; A. Ajayaghosh et al., J. Am. Chem. Soc. 2006, 128, 7174; A. Ajayaghosh et al., J. Am. Chem. Soc. 2006, 128, 7542.
Formula 1 (R═C12H25, R═C16H33) and Formula 2 found to form stable organogels in aliphatic nonpolar hydrocarbon solvents like decane, hexane, Cyclohexane, methyl Cyclohexane, toluene etc. They emit in the blue region of the visible spectrum in the monomer state, whereas, green emission was observed for the self-assembled species. Reference may be made to A. Ajayaghosh et al., Angew. Chem. Int. Ed. 2006, 45, 456 and Angew. Chem. Int. Ed. 2007, 46, 6260-6265).
Until now, there has been no disclosure of white light emitting organogels. The challenge is to tailor the organogel in such a way to give broad emission covering the entire region from 400-700 nm with suitable chromaticity for white light emission when suitably excited.